OTTAWA—Canada’s ambassador to the United States is firing back at a group of American senators who signed a public letter containing what he calls “inflated rhetoric” about Canadian softwood lumber.

Earlier this week, 25 senators sent a letter to U.S. Trade Representative Michael Froman that alleged Canadian lumber is subsidized, unfairly traded and has had decades worth of well-documented adverse economic impacts in the U.S.

Ambassador David MacNaughton shot back July 20 in a missive of his own to U.S. Sen. Ron Wyden, saying the Americans’ letter contained concerning “mischaracterizations.”